Prior sleeves that have been deployed in cementing service have been based on the concept of providing opposed piston areas exposed to tubing pressure that are of different dimensions so that raising the tubing pressure will create a sufficient net force to in theory overcome seal friction and move the sleeve to the open position. One such design is the Halliburton Initiator Sliding Sleeve that has a larger upper seal diameter than a lower seal. Raising tubing pressure creates a net differential force and the piston is allowed to move because there is an atmospheric chamber between the upper and lower seals. The problem is that to get the lower seal to be smaller than the upper seal to create the desired net force in the needed direction, the wall of the sleeve adjacent the lower seal and the atmospheric chamber has to be reduced so that the sleeve can shift while the volume of the atmospheric chamber is reduced.
The wall of the sleeve in the area of the atmospheric chamber sees substantial differential pressure and can flex or bend. When that happens the sleeve gets stuck and the desired port opening in the housing fails to occur.
Apart from these designs there are sleeves that respond to tubing pressure with an associated piston that is open on one side to tubing pressure and on the other side to annulus pressure. Such a design is illustrated in US Publication 2011/0100643. This design cannot be used in cementing applications as the filling up of the annulus with cement can block access to annulus pressure. Furthermore, there is a leak path potential from the tubing to the annulus through a piston seal leak.
Various pressure operated sleeves for downhole use are shown in U.S. Pat. Nos. and Publications: 7,703,510; 3,662,834; 4,330,039; 6,659,186; 6,550,541; 5,355,959; 4,718,494; 7,640,988; 6,386,289; US 2010/0236781 A1; U.S. Pat. Nos. 5,649,597; 5,044,444; 5,810,087; 5,950,733; 5,954,135; 6,286,594; 4,434,854 and 3,189,044.
What is needed and provided by the present invention is an actuation technique for a sliding sleeve to open a port that responds to tubing pressure but addresses the flexing or bending problem associated with prior designs so that reliable movement of the sleeve is obtained. In the preferred embodiment the application of pressure to a predetermined level actually holds the sleeve closed because the piston area on the sleeve bottom at 31 is greater than the piston area at the top of the sleeve at 32. Doing this allows the sleeve wall near the atmospheric or low pressure chamber to be strong enough to resist bending or buckling under a predetermined differential pressure. When the pressure is built up access is provided to a piston on the sleeve that is referenced to a low pressure or atmospheric chamber. This can be done with breaking a rupture disc. The sleeve can then move to open the port or ports for annulus access so that tools can be pumped down with flow without having to perforate the casing which can save a run in the hole with a perforating gun. Those skilled in the art will better appreciate more aspects of the invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.